Silicon recovery method

Abstract

The invention relates to a silicon recovery method, which comprises the following steps of: 1, recovering most silicon sludge generated by a silicon crystal process; 2, purifying the silicon sludge to form most of silicon sand; 3, conveying each silica sand into a first feed trough, wherein the first feed trough is provided with a preset airtight value and a preset air pressure value; 4, each silica sand enters a first reaction tank under the action of the preset airtight value and the preset air pressure value, the first reaction tank is connected with first heating equipment, a first preset temperature is set by the first heating equipment, alkali liquor with a preset volume is provided to enter the first reaction tank to react with each silica sand, and the first reaction tank is connected with the second heating equipment; after the reaction generates interlocking and then a self-reaction occurs, the first heating equipment is turned off; 5, hydrogen is generated when the alkali liquor reacts with the silica sand, and the hydrogen is output and stored in a storage tank; and 6, forming sodium silicate after the silica sand and the alkali liquor are reacted, and conveying the sodium silicate to an aging temporary storage tank.

Description

Technical Field

[0001] The present invention relates to a recycling method, in particular to a method for recycling waste silicon. Background Art

[0002] After the growth of semiconductor and solar silicon wafers is completed, they will first go through the steps of cutting the head and tail, then use diamond grinding wheels to grind the outer diameter until the diameter reaches the required size, and then use metal cutting wires to cut the silicon crystal rods into chips after flattening to fix the crystallization direction of the wafer. Finally, after rounding, grinding and polishing, the silicon chips required for semiconductor IC technology can be obtained. In these processes, the silicon crystal process will gradually consume the wafers, and on average, more than 40% (1 / 3) of the silicon wafers are lost (Kerf-loss). These consumed silicon wafers are discarded in the form of sludge; in addition, the global solar panels are currently facing a service life of nearly 20 years. The metallic luster material in the middle is also silicon wafers, which can be recycled and reused instead of being discarded at will.

[0003] However, existing silicon recycling technology is still limited by bottlenecks such as grinding quality, reaction design, and reaction rate, which makes it impossible to improve the quality of silicon recycling. At the same time, it is also impossible to operate continuously and adjust the quality, which greatly reduces the types and value of recycling.

[0004] In addition, existing silicon recovery technologies also have the following disadvantages:

[0005] 1. Unstable reaction rate. 2. Low Baume degree. 3. Unable to accurately adjust the number of moles. 4. Strict feeding conditions. 5. Insufficient safety. 6. Only batch production. 7. Unable to stably produce by-product hydrogen.

[0006] Based on this, how to eliminate the above defects is the technical difficulty that the inventor of the present invention wants to solve; based on many years of experience in related fields, the inventor of the present invention has conducted painstaking research and improvements for many years, and finally successfully developed and completed the present invention, and the present invention was born to improve the effect. Summary of the invention

[0007] Based on the above-mentioned shortcomings, the silicon recovery method of the present invention comprises the following steps: recovery: recovering the majority of silicon sludge generated by the silicon crystal process; purification: purifying each of the silicon sludges to form a majority of silicon sands; feeding: transporting each of the silicon sands to a first feeding trough, and the first feeding trough is provided with a predetermined airtightness value and a predetermined air pressure value; reaction: each of the silicon sands enters a first reaction trough under the action of the predetermined airtightness value and the predetermined air pressure value, and the first reaction trough is connected to a first heating device, and a first predetermined temperature is set by the first heating device, and a predetermined volume of alkali solution is provided to enter the first reaction trough to react with each of the silicon sands, and after the reaction occurs and generates an interlocking reaction, the first heating device is turned off; hydrogen storage: hydrogen is generated when the alkali solution reacts with the silicon sand, and the hydrogen is output and stored in a storage tank; and aging: sodium silicate is formed after the reaction of each of the silicon sands with the alkali solution is completed, and the sodium silicate is transported to an aging temporary storage tank.

[0008] The first feeding trough is further connected to at least one pipe body, and the pipe body is used to transport nitrogen or carbon dioxide into the first feeding trough.

[0009] The alkali solution is stored in a feeding device connected to the bottom of the first reaction tank. The feeding device includes a pump, which is used to set the concentration and flow rate of the alkali solution and allows the alkali solution to enter the first reaction tank from the bottom of the first reaction tank, thereby controlling the reaction rate of the silica sand and the alkali solution.

[0010] The first reaction tank is connected to a cooling device, and the temperature in the first reaction tank is reduced by the cooling device.

[0011] The hydrogen is further purified by a gas purification device before being input into the storage tank.

[0012] Another embodiment of the present invention is a silicon recovery method, the steps of which include: recovery: recovering a majority of silicon sludge generated by a silicon crystal process; purification: purifying each of the silicon sludges to form a majority of silicon sands; feeding: transporting each of the silicon sands to a first feeding trough, a second feeding trough and a third feeding trough, respectively, and setting a predetermined air tightness value and a predetermined air pressure value for the first feeding trough, the second feeding trough and the third feeding trough, respectively; reaction: each of the silicon sands is acted upon by the predetermined air tightness value and the predetermined air pressure value and enters a first reaction trough, a second reaction trough and a third reaction trough, respectively, the first reaction trough, the second reaction trough and the third reaction trough are respectively connected to a heating device, each of the heating devices is respectively set to a first predetermined temperature, a second predetermined temperature and a third predetermined temperature, and provides a predetermined volume of alkali solution to enter the first reaction trough and react with each of the silicon sands, and after the reaction occurs and generates an interlocking reaction, the reaction is self-contained, and then the reaction is closed. A first heating device; alkali solution overflow: the alkali solution overflows from the first reaction tank to the second reaction tank and the third reaction tank in sequence, so that the alkali solution reacts with each silica sand in the second reaction tank and the third reaction tank respectively, and the second reaction tank and the third reaction tank maintain the second predetermined temperature and the third predetermined temperature, so that each silica sand in the second reaction tank and the third reaction tank fully reacts with the alkali solution; hydrogen storage: hydrogen is generated when the alkali solution reacts with each silica sand, and the hydrogen is output and stored in a storage tank; cleaning: after each silica sand in the first reaction tank completes the reaction with the alkali solution, the residue in the first reaction tank is discharged, and an inert gas is blown into the first reaction tank, so that the first reaction tank provides another silica sand; aging: after each silica sand in the second reaction tank and the third reaction tank completes the reaction with the alkali solution, sodium silicate is formed, and the sodium silicate is transported to an aging temporary storage tank.

[0013] The first feed trough, the second feed trough and the third feed trough are also connected to at least one pipe body, and the pipe body is used to transport nitrogen or carbon dioxide into the first feed trough, the second feed trough and the third feed trough respectively.

[0014] The alkali solution is stored in a feeding device connected to the bottom of the first reaction tank. The feeding device includes a pump, which is used to set the concentration and flow rate of the alkali solution and allows the alkali solution to enter the first reaction tank from the bottom of the first reaction tank, thereby controlling the reaction rate of the silica sand and the alkali solution.

[0015] Among them, a first overflow pipe is provided between the first reaction tank and the second reaction tank, and a second overflow pipe is provided between the second reaction tank and the third reaction tank. After the alkali liquid enters the first reaction tank, it enters at least one of the second reaction tanks through the first overflow pipe, and the alkali liquid in the second reaction tank enters the third reaction tank through the second overflow pipe.

[0016] One end of the first overflow pipe and one end of the second overflow pipe are respectively arranged at the bottom of the second reaction tank and the third reaction tank, so that the alkali solution enters from the bottom of the second reaction tank and the third reaction tank respectively.

[0017] The first reaction tank, the second reaction tank and the third reaction tank are respectively connected to a cooling device, and the temperature in the first reaction tank, the second reaction tank and the third reaction tank is reduced by the cooling device.

[0018] The hydrogen is further purified by a gas purification device before being input into the storage tank.

[0019] The main purpose of the present invention is to provide a silicon recovery method, which purifies the recycled waste silicon sludge through pretreatment in the front stage of the process, and then enters the present invention to add the raw material from the feed tank to the reactor, and reacts with the continuously added reactants in the reaction tank to generate products and by-products. The main reaction formula is as follows:

[0020] Si(s)+2NaOH(aq)+H2O(l)→Na2O·nSiO2(aq)+2H2(g)

[0021] Where n in nSiO2 is the number of moles.

[0022] The main purpose of the present invention is to ensure that the quality of the product of the above reaction meets the standard and the output is stable, while improving the reaction efficiency and recovery rate.

[0023] The device used in the silicon recovery method of the present invention can be regarded as (including) a composite unit, each unit includes a feed tank, a reaction tank and corresponding valves, pipelines, weighing instruments and other control elements. The reaction unit (reaction tank) should be equipped with a corresponding number of units according to the different recovery and cleaning processes of silicon mud sources. The number of units is temporarily taken as 4 groups for the convenience of reaction description.

[0024] At the same time, pressure-maintaining devices, alkali solution feeding devices, reaction aging tanks (temporary storage tanks), heating equipment and other devices are required to facilitate production. The separated gas can enter the gas purification device or the fuel gas system for reuse. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 FIG. 1 is a schematic diagram of the architecture of the first embodiment of the present invention.

[0026] Figure 2 This is a flow chart of the first embodiment of the present invention.

[0027] Figure 3 FIG. 2 is a schematic diagram of the architecture of the second embodiment of the present invention.

[0028] Figure 4 This is a flow chart of the second embodiment of the present invention.

[0029] Among them, 10, the first feeding trough; 11, the first reaction trough; 20, the second feeding trough; 21, the second reaction trough; 30, the third feeding trough; 31, the third reaction trough; A, the tube body; B, the pump; C, the storage tank; D, the aging temporary storage tank; E, the first overflow pipe; F, the second overflow pipe. DETAILED DESCRIPTION

[0030] In order to facilitate the description of the content and the objectives that can be achieved by the present invention, specific embodiments are listed with reference to the accompanying drawings. Figure 1 and Figure 2 The silicon recovery method of the present invention comprises the following steps:

[0031] Recycling: Recycle most of the silicon sludge generated by the silicon crystal process.

[0032] Purification: The silicon sludge is purified to form a plurality of silicon sands, wherein the purification includes flushing, sedimentation and filtration, but is not limited thereto.

[0033] Feeding: Each silica sand is transported to a first feeding trough 10, and the first feeding trough is provided with a predetermined airtightness value and a predetermined air pressure value, wherein the first feeding trough 10 is also connected to at least one pipe body A, through which a nitrogen gas or a carbon dioxide gas is transported into the first feeding trough 10.

[0034] Reaction: Each silica sand enters a first reaction tank 11 under the influence of the predetermined airtightness value and the predetermined air pressure value of the first feeding tank 10. The first reaction tank 11 is connected to a first heating device. A first predetermined temperature is set by the first heating device, and a predetermined volume of alkali solution is provided to enter the first reaction tank 11 to react with each silica sand. In this embodiment, the alkali solution is NaOH. After the reaction occurs and the interlock is generated, the reaction is completed by itself, and then the first heating device is turned off.

[0035] The reaction formula of the alkali solution and the silica sand is:

[0036] Si(s)+2NaOH(aq)+H2O(l)→Na2O·nSiO2(aq)+2H2(g)

[0037] Where n in nSiO2 is the number of moles.

[0038] The alkali solution is stored in a feeding device, which is connected to the bottom of the first reaction tank 11. The feeding device includes a pump B. The concentration and flow rate of the alkali solution are set by the pump B, and the alkali solution is allowed to enter the first reaction tank 11 from the bottom of the first reaction tank 11, thereby controlling the reaction rate of the silica sand and the alkali solution and improving the safety during the reaction.

[0039] The first reaction tank 11 is also connected to a cooling device. When the temperature in the first reaction tank 11 is too high, the cooling device is used to lower the temperature in the first reaction tank 11 .

[0040] Storing hydrogen: When the alkali solution reacts with the silica sand, hydrogen is generated, and the hydrogen is output and stored in a storage tank C, wherein the hydrogen is further purified by a gas purification device before being input into the storage tank C.

[0041] Aging: After the silica sand and the alkali solution have reacted, sodium silicate is formed, and the sodium silicate is transported to an aging temporary storage tank D.

[0042] Please refer to Figure 3 and Figure 4 , which is the second embodiment of the present invention. Since the main steps are the same as those of the first embodiment, the similarities will not be repeated here.

[0043] After the silicon sludge is recovered and purified to become silicon sand, in this embodiment, in order to allow the silicon sand and the alkali solution to react fully, a continuous reaction method is adopted.

[0044] Feeding: The silica sands are transported to a first feeding trough 10, a second feeding trough 20 and a third feeding trough 30, respectively, and a predetermined airtightness value and a predetermined air pressure value are set for the first feeding trough 10, the second feeding trough 20 and the third feeding trough 30, respectively.

[0045] The first feed trough 10, the second feed trough 20 and the third feed trough 30 are also connected to at least one pipe A, through which nitrogen or carbon dioxide is transported into the first feed trough 10, the second feed trough 20 and the third feed trough 30 respectively.

[0046] Reaction: Each silica sand is affected by the predetermined airtightness value and the predetermined air pressure value and enters a first reaction tank 11, a second reaction tank 21 and a third reaction tank 31 respectively. The first reaction tank 11, the second reaction tank 21 and the third reaction tank 31 are respectively connected to a heating device. Each heating device is set to a first predetermined temperature, a second predetermined temperature and a third predetermined temperature respectively, and provides a predetermined volume of alkali solution to enter the first reaction tank 11 and react with each silica sand. After the reaction occurs and generates an interlock, the reaction is completed by itself, and then the first heating device is turned off.

[0047] The alkali solution is stored in a feeding device, which is connected to the bottom of the first reaction tank 11. The feeding device includes a pump B. The concentration and flow rate of the alkali solution are set by the pump B, and the alkali solution is allowed to enter the first reaction tank 11 from the bottom of the first reaction tank 11, thereby controlling the reaction rate of the silica sand and the alkali solution.

[0048] Alkaline solution overflow: the alkali solution overflows from the first reaction tank 11 to the second reaction tank 21 and the third reaction tank 31 in sequence, so that the alkali solution reacts with the silica sands in the second reaction tank 21 and the third reaction tank 31 respectively, and the second reaction tank 21 and the third reaction tank 31 maintain the second predetermined temperature and the third predetermined temperature, so that the silica sands in the second reaction tank and the third reaction tank fully react with the alkali solution, and the hydrogen generated in the reaction process is also stored in the storage tank C, wherein the hydrogen is further purified by a gas purification device before being input into the storage tank.

[0049] A first overflow pipe is provided between the first reaction tank 11 and the second reaction tank 21, and a second overflow pipe is provided between the second reaction tank 21 and the third reaction tank 31. After the alkali liquid enters the first reaction tank 11, it enters at least one of the second reaction tanks 21 through the first overflow pipe, and the alkali liquid in the second reaction tank 21 enters the third reaction tank 31 through the second overflow pipe.

[0050] One end of the first overflow pipe and one end of the second overflow pipe are respectively arranged at the bottom of the second reaction tank 21 and the third reaction tank 31, so that the alkali solution enters from the bottom of the second reaction tank 21 and the third reaction tank 31 respectively. In other words, the other ends of the first overflow pipe and the second overflow pipe are respectively connected to the first reaction tank 11 and the second reaction tank 21, so that the two ends of the first overflow pipe and the second overflow pipe form a high-low configuration to ensure that the alkali solution flows from high to low.

[0051] Cleaning: After the silica sand in the first reaction tank 11 has completed the reaction with the alkali solution, the residue in the first reaction tank 11 is discharged, and an inert gas is blown into the first reaction tank 11 so that the first reaction tank 11 can receive another silica sand and the alkali solution and silica sand react again.

[0052] Aging: After the silica sand in the second reaction tank 21 and the third reaction tank 31 reacts with the alkali solution, sodium silicate is formed, and the sodium silicate is transported to an aging temporary storage tank D.

[0053] In other words, the silica sand that has been pre-treated is put into the first feed trough 10, the second feed trough 20 and the third feed trough 30, and the sealing gas pressure is adjusted so that the raw materials (silica sand) in the first feed trough 10, the second feed trough 20 and the third feed trough 30 can fall smoothly into the first reaction trough 11, the second reaction trough 21 and the third reaction trough 31 below, respectively, and the pump B is started to pump the alkali solution. At the initial stage of feeding, the first reaction trough 11, the second reaction trough 21 and the third reaction trough 31 need to be heated. After the reaction occurs and the interlocking reaction occurs, the reaction is self-contained and a certain reaction temperature is maintained. Then, it is not necessary to provide the first feed trough 10 and the first reaction trough 11 with heat sources. In order to confirm the completeness of the reaction, the second reaction trough and the third reaction trough will be provided with heat sources by the heating device to maintain a certain reaction temperature to ensure that the alkali solution reacts completely. Similarly, when the reaction is over-excited, the cooling device is also used to provide ice water to control the reaction temperature in time.

[0054] The concentration and flow rate of the fluid (alkaline solution) in the reaction are another key point in controlling the reaction rate. Due to safety considerations, the first reaction tank 11, the second reaction tank 21 and the third reaction tank 31 are not equipped with any stirring device. The main stirring comes from the feeding of the fluid (alkaline solution) below, and then enters the second reaction tank 21 and the third reaction tank 31 through the first overflow pipe and the second overflow pipe respectively. This process is repeated and finally enters the reaction aging tank (aging temporary storage tank D) for testing to determine whether the product is compliant or not, or needs to return to the reactor, and finally reaches a steady state and becomes a compliant product.

[0055] In the second embodiment, the first reaction tank 11 will not fully participate in the reaction but will perform the feeding operation of the first feeding tank 10. In principle, the raw material silica sand of the first reaction tank 11 that first contacts the fresh alkali solution will be used up the fastest. Judging from the reaction temperature, the opening of the gas outlet constant pressure valve and the external heat supplement, it can be determined that the silica sand should have been fully reacted, so the remaining residue is discharged and the feeding operation is performed. After the feeding is completed and the inert gas is blown for multiple times, the first reaction tank 11 can enter the standby state and participate in the reaction at any time, so continuous production can be completed without interruption, which is conducive to the development and design of the back-end process.

[0056] The silicon recovery method of the present invention converts the waste silicon sludge into high-value raw materials instead of discarding them at will, and can also produce by-product hydrogen to increase the utilization value of the recovered products. The advantages of the present invention include: 1. The reaction rate is stable. 2. The Baume degree is equivalent to that on the market and can be adjusted according to customer requirements. 3. The number of moles can be adjusted in the middle of the reaction. 4. The particle size and quality of the silica sand do not need to be strictly restricted. 5. The rotating equipment is greatly reduced, and there is no power stirring device. 6. Continuous production. 7. The by-product hydrogen can be stably produced and is suitable for reuse.

[0057] The above detailed description is a specific description of a feasible embodiment of the present invention, but the embodiment is not intended to limit the patent protection scope of the present invention. Any equivalent implementation or modification that does not deviate from the technical spirit of the present invention should be included in the patent protection scope of the present invention.

Claims

1. A silicon recovery method, characterized in that: The steps include: Recycling: Recycling most of the silicon sludge produced by the silicon crystal process; Purification: The silicon sludge is purified to form a large amount of silicon sand; Feeding: each silica sand is transported to a first feeding trough, and the first feeding trough is provided with a predetermined airtightness value and a predetermined air pressure value; Reaction: Each silica sand is subjected to the predetermined airtightness value and the predetermined air pressure value and enters a first reaction tank, the first reaction tank is connected to a first heating device, a first predetermined temperature is set by the first heating device, and a predetermined volume of alkali solution is provided to enter the first reaction tank to react with each silica sand, and after the reaction occurs and the interlocking reaction is completed, the first heating device is turned off; Storing hydrogen: when the alkali solution reacts with the silica sand, hydrogen is generated, and the hydrogen is output and stored in a storage tank; and Aging: After the silica sand and the alkali solution have reacted, sodium silicate is formed, and the sodium silicate is transported to an aging temporary storage tank.

2. The silicon recovery method according to claim 1, characterized in that: The first feeding trough is also connected to at least one pipe body, through which nitrogen or carbon dioxide is transported into the first feeding trough.

3. The silicon recovery method according to claim 1, characterized in that: The alkali solution is stored in a feeding device connected to the bottom of the first reaction tank. The feeding device includes a pump. The concentration and flow rate of the alkali solution are set by the pump, and the alkali solution is allowed to enter the first reaction tank from the bottom of the first reaction tank, thereby controlling the reaction rate of the silica sand and the alkali solution.

4. The silicon recovery method according to claim 3, characterized in that: The first reaction tank is connected to a cooling device, and the temperature in the first reaction tank is reduced by the cooling device.

5. The silicon recovery method according to claim 1, characterized in that: The hydrogen is further purified by a gas purification device before being input into the storage tank.

6. A silicon recovery method, characterized in that: The steps include: Recycling: Recycling most of the silicon sludge produced by the silicon crystal process; Purification: The silicon sludge is purified to form a large amount of silicon sand; Feeding: transporting each silica sand to a first feeding trough, a second feeding trough and a third feeding trough respectively, and setting a predetermined airtightness value and a predetermined air pressure value of the first feeding trough, the second feeding trough and the third feeding trough respectively; Reaction: Each of the silica sands is subjected to the predetermined airtightness value and the predetermined air pressure value and enters a first reaction tank, a second reaction tank and a third reaction tank respectively. The first reaction tank, the second reaction tank and the third reaction tank are respectively connected to a heating device, each of the heating devices is respectively set to a first predetermined temperature, a second predetermined temperature and a third predetermined temperature, and provides a predetermined volume of alkali solution to enter the first reaction tank and react with each of the silica sands. After the reaction occurs and the interlocking reaction is completed, the first heating device is turned off; Alkaline solution overflow: the alkali solution overflows from the first reaction tank to the second reaction tank and the third reaction tank in sequence, so that the alkali solution reacts with the silica sands in the second reaction tank and the third reaction tank respectively, and the second reaction tank and the third reaction tank maintain the second predetermined temperature and the third predetermined temperature, so that the silica sands in the second reaction tank and the third reaction tank fully react with the alkali solution; Storing hydrogen: when the alkali solution reacts with the silica sand, hydrogen is generated, and the hydrogen is output and stored in a storage tank; Cleaning: After the silica sand in the first reaction tank has finished reacting with the alkali solution, the residue in the first reaction tank is discharged, and the inside of the first reaction tank is blown with an inert gas so that the first reaction tank can receive another silica sand; Aging: After the silica sand in the second reaction tank and the third reaction tank reacts with the alkali solution, sodium silicate is formed, and the sodium silicate is transported to an aging temporary storage tank.

7. The silicon recovery method according to claim 6, characterized in that: The first feed trough, the second feed trough and the third feed trough are also connected with at least one pipe body, and the pipe body is used to transport nitrogen or carbon dioxide into the first feed trough, the second feed trough and the third feed trough respectively.

8. The silicon recovery method according to claim 6, characterized in that: The alkali solution is stored in a feeding device connected to the bottom of the first reaction tank. The feeding device includes a pump. The concentration and flow rate of the alkali solution are set by the pump, and the alkali solution is allowed to enter the first reaction tank from the bottom of the first reaction tank, thereby controlling the reaction rate of the silica sand and the alkali solution.

9. The silicon recovery method according to claim 8, characterized in that: A first overflow pipe is provided between the first reaction tank and the second reaction tank, and a second overflow pipe is provided between the second reaction tank and the third reaction tank. After the alkali liquid enters the first reaction tank, it enters at least one of the second reaction tanks through the first overflow pipe, and the alkali liquid in the second reaction tank enters the third reaction tank through the second overflow pipe.

10. The silicon recovery method according to claim 9, characterized in that: One end of the first overflow pipe and one end of the second overflow pipe are respectively arranged at the bottom of the second reaction tank and the third reaction tank, so that the alkali solution enters from the bottom of the second reaction tank and the third reaction tank respectively.

11. The silicon recovery method according to claim 9, characterized in that: The first reaction tank, the second reaction tank and the third reaction tank are respectively connected to a cooling device, and the temperature in the first reaction tank, the second reaction tank and the third reaction tank is reduced by the cooling device.

12. The silicon recovery method according to claim 6, characterized in that: The hydrogen is further purified by a gas purification device before being input into the storage tank.

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